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Article

Use of Food Attractant to Monitor and Forecast Population Dynamics of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a Long-Distance Migratory Pest

by
Lingyun Gao
1,2,†,
Ran Yan
3,†,
Wei He
4 and
Kongming Wu
3,*
1
College of Plant Protection, Henan Agricultural University, Zhengzhou 450002, China
2
The Laboratory of Lingnan Modern Agriculture, Guangzhou 510000, China
3
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China
4
State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Agriculture and Forestry University, Fuzhou 350002, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2023, 13(8), 2141; https://doi.org/10.3390/agronomy13082141
Submission received: 22 July 2023 / Revised: 13 August 2023 / Accepted: 14 August 2023 / Published: 16 August 2023
(This article belongs to the Section Pest and Disease Management)
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Abstract

:
The rice leaf folder, Cnaphalocrocis medinalis, is a significant migratory pest that restricts rice production in Asia and Africa, and monitoring and early warning measures are the basis for its management. Based on its regional migratory path in China, the pest population dynamics were monitored from 2020 to 2021 using food attractants. In this study, we also used internal reproductive system dissection to determine the adult age and reproductive developmental state. The monitoring results indicated that the trapping dynamics of C. medinalis males using food attractants and sex pheromones were approximately similar. Both trapping methods yielded C. medinalis males of different ages, with an identical age structure for both trap types. Dissection analysis of the reproductive system of females trapped using the food attractants indicated that in 2020, the population of C. medinalis in Liling, Hunan Province, was indigenous, while populations in other monitoring sites mainly comprised migrants from other areas. The ovarian development level of females trapped using food attractants showed a positive correlation with the age of males, and there was also a significant positive correlation between the index of ovarian development of females and the mating time. Furthermore, a dynamic prediction method for fecundity in field populations was established based on the quantity of eggs held by the females. This study provides a new method for the monitoring and early warning of the existence of C. medinalis populations.

1. Introduction

Rice is one of the world’s major food crops, with about 3 billion people worldwide relying on rice as a staple food. The rice leaf folder, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), is one of the most significant pests affecting rice. The larvae prefer to feed on young rice leaves, often causing white streaks on the surface, which affects leaf photosynthesis, leading to an increase in the rate of rice blight and a decrease in grain weight [1,2,3]. Frequent outbreaks of C. medinalis in many Asian countries such as China, India, and Japan have caused huge losses to Asian rice production [4,5,6,7,8]. C. medinalis caused 5%–25% annual rice losses in Bangladesh [9]. From 1991 to 2019, the average annual area of occurrence of C. medinalis in China was 16.05 × 108 ha, accounting for 66.3% of the rice planting area, resulting in a rice loss of 70.27 × 108 kg [10,11].
C. medinalis has a long-distance migratory habit; Fu et al. used radar to monitor the migration dynamics of C. medinalis in the Bohai Bay area [12] and provided the flight speed, flight altitude, and migration duration of C. medinalis. C. medinalis exhibits a north-south migration pattern in East Asia and migrates northward from southern overwintering areas in five large-scale northward migrations every spring and summer, which is harmful to the vast rice areas south of the Huaihe River in China’s Qinling Mountains. As autumn temperatures drop and rice ripens in northern China, C. medinalis embarks upon three large-scale migrations southward, harming the Jianghuai, Jiangling, and Hainan perennial rice areas [13]. The main method of controlling C. medinalis is the application of chemical pesticides, but long-term overuse of chemical pesticides often leads to increased pest resistance, environmental pollution, and other problems [14]. Understanding the migration pattern of C. medinalis can predict the time of insect outbreak damage and improve control efficiency.
Currently, the commonly used monitoring methods for adult C. medinalis are moth repellent methods, searchlight trapping methods, and sex pheromone trapping methods [15,16]. The moth count using the moth repellent method is not easily obtained, and the correlation between the number of moths and the actual population density in the field is low [17]. Due to the weak phototaxis of adult C. medinalis, the searchlight trapping method cannot accurately reflect the population dynamics of C. medinalis [18]. Sex pheromone monitoring is widely used in the monitoring of C. medinalis, as it possesses high specificity and sensitivity [19,20,21]. However, pheromone-based trapping can only trap C. medinalis males; it does not accurately predict fecundity and offspring larva numbers based on C. medinalis female dynamics [22,23].
Food attractants based on the pest’s preferred food source possess the advantages of high specificity and sensitivity, as well as the ability to trap both female and male pests [24,25]. Previous studies have shown that valeraldehyde, benzaldehyde, and methyl salicylate are attractive to C. medinalis, and further studies have shown that benzaldehyde, phenylacetaldehyde, and methyl salicylate have the strongest attraction to C. medinalis at a concentration of 10 g/L [26,27].
Previous studies have shown that food attractants display a good trapping effect on adult C. medinalis in the field [28,29], but the reproductive development status and prediction methods of adult C. medinalis have not been thoroughly investigated. Based on trapping adult C. medinalis in the field using food attractants and employing internal reproductive system dissection, we aim to determine the adult reproductive development state and to establish a monitoring and early warning method for the C. medinalis population. This study could also provide new technical means to further improve the level of surveillance and early warning technology to guide the precise prevention and control of C. medinalis.

2. Materials and Methods

2.1. Experimental Materials and Methods

Field monitoring trials were conducted in Guangxi, Hunan, Jiangsu, and Zhejiang provinces, China, in 2020 and 2021, and the specific test locations and test duration are shown in Table 1. During the 2020 monitoring period, one rice field in seven different sites in Guangxi, Hunan, Jiangsu and Zhejiang provinces, each with an area of 1334 m2, with uniform growth and consistent field management, was selected as the experimental field. Six bell inverted funnel traps (height 364 mm, diameter 264 mm, consisting of three parts: insect collection barrel, inverted funnel, and core lure handle), with food attractants, were placed equidistantly in the center of each experimental field, according to the standard of one trap per 50 m. In the experimental fields of Zhangjiagang, Jiangsu Province, and Liling, Hunan Province, in addition to traps equipped with food attractants, six bell inverted funnel traps with sex pheromones were placed as controls, and the traps using two different baits were separated by 100 m. During the monitoring period in 2021, one experimental field, with an area of 1334 m2, was selected in three different sites in Hunan and Jiangxi provinces. Six bell inverted funnel traps, fitted with food attractants, were placed equidistant in the center of each test field. In Shaodong, Hunan Province, in addition to placing traps baited with food attractants, six bell inverted funnel traps with sex pheromones were also placed as a control.
The C. medinalis food attractant (ingredients and ratio: methyl salicylate:limonene:camphor = 1:0.5:2.5) was a solid block [28], with an active ingredient content of 4 g/package. C. medinalis sex pheromones were composed of Z13-18: Ald, Z11-18: Ald, Z13-18: OH, and Z11-18: OH, at a 500:60:120:60 ratio [14], with 740 μg/pc active ingredient provided on a PVC capillary. Bell inverted funnel traps were fixed at 50 cm above the rice plant, and the height was adjusted regularly with the growth of the plant. The food attractants were replaced once every 15 days, and the sex pheromones were changed once every 30 days. The bell inverted funnel traps, food attractants, and pheromones were provided by Shenzhen Bioglobal Agricultural Science Co., Ltd. (Shenzhen, China). This is a company focused on green pest management, and its food attractant products for use with agricultural pests, such as Helicoverpa armigera and Spodoptera frugiperda, indicate good prospects for pest monitoring [30,31].
The number of adult C. medinalis females and males per trap was investigated every morning, and all trapped C. medinalis were transferred to the laboratory for dissection and determination of reproductive development status. On a daily basis, up to 50 male and female individuals (per type of attractant) were dissected, and all were dissected if the trapping number was less than 50.

2.2. Methods of Adult Dissection and Determination of the Age of Males

Referring to the anatomical methods of Feng et al. [23], adult C. medinalis trapped with food attractants and sex pheromones in the field were dissected every day. The adult abdomen was cut with a pair of scissors (12 cm long), placed in a Petri dish (5 cm diameter), and the abdominal body wall was torn through the fracture under a TS75-X trinocular microscope (Shanghai Shangguang New Optical Technology Co., Ltd. Shanghai, China) to separate the ovaries (Figure 1A) and testes (Figure 1D). Next, the testes were removed and placed in a 5 cm diameter plastic Petri dish filled with saline solution. The Petri dish was placed under a stereoscope (TS-75X; Shanghai Shangguang New Optical Technology Co., Ltd., Shanghai, China), and the major axis length of the testis (i.e., testis size) was measured with an OLD-SGD imaging system (Shanghai Shangguang New Optical Technology Co., Ltd.). The age of the males was judged by referring to the dividing criteria of C. medinalis (Table 2) suggested by Chen et al. [32]. After completion of the ovarian dissection, the index of ovarian development and the number of mating times (number of spermatophore in the bursa copulatrix) were determined and recorded by referring to the ovarian development classification criteria of Zhang et al. [33]. The number of spermatophores (Figure 1C) in the bursa copulatrix (Figure 1B) of female C. medinalis can indicate the number of mating times. That is, the presence of X spermatophores in the bursa copulatrix indicates mating X times [23].

2.3. Determination of Adult Source Properties and Dynamic Prediction of Oviposition

Referring to Zhang et al. [33], the property of insect origin of C. medinalis was determined by the following criteria: if the proportion of individuals with an index of ovarian development of 1 regarding females trapped using food attractants is 10%–30%, and the proportion of individuals with an index of ovarian development of 3–5 is 30%–62.18% during the monitoring period, then the population of C. medinalis at the experimental site is a native population. If the proportion of individuals with an index of ovarian development of 3–5 of females trapped using food attractants is about 80% or more, the population of C. medinalis at the experimental site is mainly a migrant population from other regions.
Prediction of egg-laying dynamics of females: based on the ovarian development law of females of C. medinalis [33], the females exhibit the highest amount of egg holding when the ovaries develop to grade 3, and this result can be used as the total egg amount of the females before egg laying. The egg yield of a female in the field on a given day can be calculated using the following formula:   p = 1 − X N . In the formula, p is the percent of oviposition of females in the field on a given day; X is the average number of eggs held by females trapped using food attractants on a certain day; N is the average egg holding capacity of C. medinalis trapped in the field with an index of ovarian development of 3. The daily percent of oviposition of females during the monitoring period was calculated to obtain the oviposition dynamics of females in the field.

2.4. Statistical Analysis

A Student’s t-test was used to compare the daily trap counts between traps with food attractants and those with sex pheromones. A Chi-square test was used to assess differences in the sex ratio of female to male (1:1), as well as the male age structure for individuals caught in traps using food lures or sex pheromones. Pearson correlation analysis was used to compare the index of ovarian development, age of males, and number of matings. All data were analyzed using SPSS 26.0 (IBM, Armonk, NY, USA).

3. Results

3.1. Comparison of Monitoring Effects of Food Attractants and Sex Pheromones

The peak in both the food attractant and sex pheromone mediated monitoring of C. medinalis in Liling occurred in mid-July (Figure 2A), while the peak of both food attractant and sex pheromone monitoring of C. medinalis in Zhangjiagang occurred twice: once in late July and once in late August (Figure 2B). At the two sites, the peak occurrence of C. medinalis was essentially the same using either of the two trapping methods. At Shaodong in 2021, C. medinalis monitored using food attractants showed one peak period in early July, and those monitored using sex pheromones also exhibited one peak period in early July (Figure 2C). The peak period of C. medinalis was essentially the same for both food attractant and sex pheromone monitoring, but the peak period for sex pheromone monitoring was longer, and the number of trappings was higher in early and mid-July.
In 2020 in Liling, a total of 4142 adult C. medinalis were trapped using food attractants, and 253 adult C. medinalis were trapped using sex pheromones. A total of 2569 adults were trapped using food attractants, and 211 adults were trapped using sex pheromones in Zhangjiagang. Food-based trapping thus yielded a higher daily trap capture than pheromone-based approaches in Liling and Zhangjiagang (Liling: t = 8.46, df = 60, p < 0.05; Zhangjiagang: t = 6.81, df = 48, p < 0.05). In 2021, a total of 6615 adults were trapped using food attractants, and 6429 adults were trapped using sex pheromones. There was no significant difference in the average daily trapping amount of C. medinalis using food attractants or sex pheromones in Shaodong. (t = −1.93, df = 86, p = 0.06).
The anatomical results regarding C. medinalis males trapped during the year 2020 using food attractants and sex pheromones showed that the highest percentage of 1-day-old males trapped using food attractants and sex pheromones in Liling was 17.8% and 23.72%, respectively. The lowest percentage of 7-day-old males trapped using food attractants was 8.67%, and the lowest percentage of 8-day-old moths trapped using sex pheromones was 5.53% (Figure 2D). The highest proportion of 8-day-old males trapped using food attractants and sex pheromones in Zhangjiagang was 35.71% and 32.65%, respectively. The lowest proportion of 1-day-old males trapped by food attractants and sex pheromones was 1.02% and 2.04%, respectively (Figure 2E). Both food attractants and sex pheromones trapped males at almost all ages (i.e., 1–8 days old), and there was no significant difference in the age structure of males trapped using either trapping method (Liling: χ2 = 13.33, df = 7, p = 0.064; Zhangjiagang: χ2 = 9.264, df = 7, p = 0.234). The highest percentage of 8-day-old males trapped using food attractants and sex pheromones in Shaodong in 2021 was 27.50% and 22.50%, respectively, while that of 1-day-old males was the lowest, with both capturing 4% (Figure 2F). The age structure of field-caught males did not differ between either trapping method (Shaodong: χ2 = 4.482, df = 7, p = 0.722).
In 2020, the results of the field monitoring using food attractants in seven different locations showed significant differences in the number of females and males of C. medinalis captured in different locations. With the exception of Zhangjiagang, the number of females was higher than the number of males, and the number of males in the remaining six sites was significantly higher than the number of females (Table 3). In 2021, the number of males trapped by C. medinalis was significantly higher than that of females at the two sites, except for the number of females and males trapped using food traps in Taihe, which was not significantly different (Table 3).

3.2. Monitoring Seasonal Population Migration Dynamics of C. medinalis Using Food Attractants

During the monitoring period in 2020, the C. medinalis peak occurred in mid to late July (Figure 3B–D), except for Guigang, in which the peak of C. medinalis was observed in early June (Figure 3A). The maximum number of trapped C. medinalis was 1631/day in Shaodong, and the lowest was 220/day in Quzhou.
In 2021, the peak periods of C. medinalis at Shaodong and Zhijiang were basically the same (Figure 3E). Shaodong recorded the highest number of C. medinalis trapped on June 30, with a maximum of 883 adults per day. Zhijiang reached its highest trapping number of C. medinalis on 2 July, with a maximum of 136/day. At Taihe, there was a peak of C. medinalis in early June, and the highest trapping number was reached on June 5, with a maximum of 117/day (Figure 3E).

3.3. Monitoring the Reproductive Development Status of C. medinalis using Food Attractants

The anatomical results of females trapped using food attractants in different locations in 2020 showed that the proportion of individuals with an index of ovarian development of 1 in females trapped using food attractants in Guigang was 11.96%, and that of individuals with an index of ovarian development of 3–5 was 82.68% (Figure 4A). The proportion of individuals with an index of ovarian development of 1 trapped using food attractants in Liling was 10.92%, and the proportion of individuals with an index of ovarian development of 3–5 was 62.78% (Figure 4B). The percentage of individuals with an index of ovarian development of 1 and 3–5 in Shaodong was 0.77% and 94.59%, respectively (Figure 4C). In Changzhou, the proportion of trapped females with an index of ovarian development of 1 and 3–5 was 0 and 94.59%, respectively (Figure 4D). In Zhangjiagang, the proportion of trapped females with an index of ovarian development of 1 and 3–5 was 2.88% and 94.01%, respectively (Figure 4E). In Quzhou, the proportion of trapped females with an index of ovarian development of 1 and 3–5 was 9.30% and 77.41%, respectively (Figure 4F). In Xiangshan, the proportion of trapped females with an index of ovarian development of 1 and 3–5 was 1.60% and 94.57%, respectively (Figure 4G). Based on the criteria for determining the nature of C. medinalis origin, it can be judged that in 2020, except for the Liling C. medinalis population as a local population, the populations of C. medinalis in the other six locations were mainly migrant species.
The anatomical results of females trapped by food attractants in different locations in 2021 showed that the ovarian developmental level 1 females trapped using food attractants in Shaodong accounted for 7.44%, and the ovarian development level 3–5 females accounted for 87.18% (Figure 4H). The proportion of ovarian developmental level 1 females trapped using food attractants in Zhijiang was 2.05%, and the proportion of ovarian developmental level 3–5 females was 94.36% (Figure 4I). The number of individuals of ovarian developmental level 1 females trapped using food attractants in Taihe accounted for 2.86%, and the proportion of ovarian developmental level 3–5 females was 94.49% (Figure 4J). In 2021, the C. medinalis populations of Shaodong, Zhijiang, and Taihe were mainly species which had migrated from other locations.
The correlation analysis between the index of ovarian development of females and the male age of C. medinalis trapped using food attractants showed that there was a significant positive correlation between the index of ovarian development and the male age at Quzhou and Xiangshan in 2020, as well as Shaodong and Zhijiang in 2021. (Quzhou: r = 0.570, p = 0.007, Figure 5A; Xiangshan: r = 0.604, p = 0.002, Figure 5B; Shaodong: r = 0.401, p = 0.011, Figure 5C; Zhijiang: r = 0.527, p = 0.017, Figure 5D).
The correlation analysis of the ovarian development level and mating time of C. medinalis trapped using food attractants at different sites in 2020 and 2021 showed that the ovarian development level and mating time of females in Guigang, Liling, Zhangjiagang, and Quzhou in 2020 and Shaodong and Zhijiang in 2021 were significantly positively correlated (Guigang: r = 0.905, p < 0.001, Figure 6A; Liling: r = 0.937, p < 0.001, Figure 6B; Zhangjiagang: r = 0.837, p < 0.001, Figure 6C; Quzhou: r = 0.880, p < 0.001, Figure 6D; Xiangshan: r = 0.760, p < 0.001, Figure 6E; Shaodong: r = 0.766, p < 0.001, Figure 6F; Zhijiang: r = 0.797, p < 0.001, Figure 6G).

3.4. Prediction of Oviposition Dynamics of C. medinalis Based on Food Attractants Monitoring Data

In 2020, the egg holding amount of C. medinalis in Guigang was low during the monitoring period. The lowest egg holding volume was 9.80 ± 5.07 on May 29, and the highest egg holding volume was 56.00 ± 4.00 on June 21 (Figure 7A). The prediction of oviposition dynamics showed that the highest percentage of oviposition in Guigang was 86.00% on May 29, and the lowest was 20.00% on 21 June (Figure 7A). At Liling in 2020, the lowest egg holding capacity was 21.67 ± 3.09 on 9 July, and the highest egg holding capacity was 40.35 ± 2.65 on July 19 (Figure 7B). Liling showed a maximum percentage of oviposition of 69.05% on 9 July and a minimum percent oviposition of 42.35% on 19 July (Figure 7B).

4. Discussion

The real-time and accurate monitoring of the population dynamics of migratory pests can provide important data for prediction and control decisions, laying a solid foundation for integrated pest management concepts [34,35]. This study showed that the monitoring of insect age and reproductive development state is possible using food attractant traps. We also showed how reproductive system analysis can be used to determine the nature of the origin of C. medinalis at different sites. In addition, we investigated the relationship between ovarian development, male age, and mating time of adult C. medinalis trapped using food attractants and predicted the fecundity dynamics of C. medinalis. In addition, in this study, a new monitoring and early warning method based on food attractants trapping of C. medinalis was explored, which is valuable for guiding the regional management of this pest.
In this study, the monitoring effects of the use of food attractants and sex pheromones on C. medinalis were compared, and the results showed that the peak occurrence period of adults trapped using food attractants and sex pheromones in three different locations was basically consistent during the two-year monitoring period. However, the trapping efficiency of food attractants was superior to that of sex pheromones. For example, in 2020, the number of adults trapped using food attractants in Liling and Zhangjiagang was significantly higher than that obtained using sex pheromones. Zeng et al. trapped adult C. medinalis in different ways, and found that the number of adults trapped using food attractants was higher than that obtained using sex pheromones, and this method could trap both sexes simultaneously [28]. This result is consistent with the results of the current study using food attractants to monitor C. medinalis. We also compared the age structure of males trapped using food attractants and sex pheromones and found that almost all males of each age (1–8 days old) could be trapped using either trapping method, and there was no significant difference in the age structure of males between the two methods. This is consistent with the results obtained by He et al. using food attractants to trap adult S. frugiperda [31]. Different food attractants often result in different sex ratios when trapping different species of pests. For example, the sex ratio of Spodoptera exigua trapped using food attractants was close to 1:1 [36], while the number of female S. frugiperda trapped was significantly higher than the number of male moths [31]. This may be caused by the different volatile components of food attractants. Cheng et al. found that male C. medinalis showed strong potential responses to n-valeraldehyde, benzaldehyde, and methyl salicylate [26]. In addition, based on the monitoring results of food attractants in 2020–2021, it can be seen that the peak occurrence period of C. medinalis in different locations in the same province was basically the same. For example, in 2020, the peak periods of C. medinalis in Liling and Shaodong in Hunan Province, Changzhou and Zhangjiagang in Jiangsu Province, and Quzhou and Xiangshan in Zhejiang Province are basically the same, and the peak periods of C. medinalis in Shaodong and Zhijiang in Hunan Province in 2021 was basically the same. We infer that C. medinalis may migrate to different locations in the same province on a large scale at similar times. Therefore, the control strategy for C. medinalis must not only be limited to a single area, but needs to be managed in the pest source province for reducing its possibility of regional outbreaks by long distance migration. Insect ovary dissection technology is one of the most important methods for studying pest occurrence patterns and predicting their times of onset. By the dissection of female ovaries in the field, the process of ovarian development of females can be determined, and subsequently, the nature of insect origin can be determined [37]. In this study, by dissecting the ovaries of females trapped using food attractants, it was found that the sources of trapped C. medinalis were different in different years and places. For example, in 2020, the population of C. medinalis in Liling was a native population, and the populations of C. medinalis in the rest of the sites were mainly migrant populations from other regions. According to the migration principle, C. medinalis began migrating north from Guangxi and Hainan Province from late May to mid-June, mainly landing in the Jiangling rice area in eastern and northern China. In mid-to-late June, a large number of C. medinalis migrated from the Jiangling rice area to the vast Jianghuai rice area in the Huaihe River Basin and the Hanzhong Basin. From late July to early August, it continued to move north, reaching the northern rice areas of North and Northeast China. From late August to early September, C. medinalis began to migrate southward to the perennial rice areas of Jianghuai, Jiangling, and Hainan [38,39]. In this study, adult C. medinalis monitored in Hunan, Guangxi, Jiangsu, Zhejiang, and Jiangxi provinces were predominantly migrant populations, which were consistent with the C. medinalis north-south migration law in China. This study also showed that ovarian development was positively correlated with both the moth age and mating times of C. medinalis. Therefore, when the number of females trapped using food attractants is low, the ovarian development level of females can be inferred based on the age of male C. medinalis to accurately monitor the reproductive development status of adult C. medinalis. When anatomical samples are damaged, the accuracy of determining the ovarian development index can be improved by analyzing the mating time of female C. medinalis. Based on the egg holding capacity of female C. medinalis trapped in the field, we can also speculate on the percentage of oviposition of the C. medinalis population in the field, which is helpful in establishing a larval hatching model.
In this study, by analyzing the reproductive development status of adult C. medinalis trapped in the field using an attractant and number dynamics, the origin of the field population of C. medinalis can be more accurately explored, and fecundity dynamics can be predicted. In the future, for comprehensive control of C. medinalis, the monitoring of food attractants may be combined with physical control, and light trapping may be used to trap adults during peak periods [40]. Based on the analysis of the nature of the insect source, trapping measures along the migration path may be established to reduce migration in crop growing areas. In addition, the combination of the use of food attractants and push-pull strategies may reduce the infestation of C. medinalis, i.e., in field trials, by combining food attractants and push-pull strategies to reduce the fecundity of Drosophila suzukii and Delia radicum [41,42,43].
Similar to the results of this study, the use food attractants has also showed a strong ability to monitor other pests. For example, the use of food attractants (pear esters) in apple orchards can effectively capture female and male codling moths, and the trapping peak for the use of food attractants is consistent with those obtained using sexual attractants [44,45]. However, trapping efficiency was often low regarding the use of food attractants. For example, the average daily fall armyworm collection number was only 0.5/trap [29], and the average daily trapping number of females and males of the grape berry moth was less than 1/trap [46]. In this study, the average daily number pests trapped using food attractants was higher than that obtained using sex pheromones, providing more accurate monitoring results. Moreover, since food attractants are usually composed of plant volatiles, they are also attractive to non-target insects. For example, food attractants often trap beneficial insects, while monitoring population dynamics [47]. In this study, the proportion of C. medinalis trapped using food attractants in the field monitoring process was as high as 90%, and this method was also highly specific and less harmful to non-target insects, such as beneficial insects.
Food attractants are convenient and environment friendly, but they still exhibit some problems. Under field conditions, the effective period for C. medinalis food attractants are short, most of which are only 15–20 d [48]. Moreover, the high concentration of volatiles in food attractants at the early stage of the test resulted in some repellent effect on C. medinalis, while the decreased volatile concentration at the later stage of use reduced adult trapping, which had a greater impact on the long-term monitoring of population dynamics. Factors such as the color, shape, and height of the trap may also have an impact on trapping efficiency. Therefore, in order to improve the monitoring accuracy of food attractants, further studies are needed in terms of food attractant carrier materials, volatile compound field release rate, trap settings, and field distribution. This study showed that food attractants can accurately monitor C. medinalis population dynamics in the field. Combined with reproductive anatomy techniques, the reproductive development status and origin characteristics of C. medinalis in field populations can be further analyzed. In addition, we have established a link between the reproductive development of females and males trapped using food attractants, which can improve the accuracy of monitoring. Our research is useful in advancing the development of field population surveillance technology for C. medinalis, which is of great value to guide the regional management of this pest.

Author Contributions

Conceptualization, L.G., R.Y., W.H. and K.W.; methodology, L.G., R.Y., W.H. and K.W.; software, L.G., R.Y. and W.H.; validation, W.H. and K.W.; writing—original draft preparation, L.G.; writing, all authors; visualization, all authors; supervision, K.W.; project administration, K.W. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the Laboratory of Lingnan Modern Agriculture Project (NT2021003).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Data sharing is not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

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Figure 1. Anatomy of reproductive organs of C. medinalis. Ovary (A); bursa copulatrix (B); spermatophore (C); testis (D).
Figure 1. Anatomy of reproductive organs of C. medinalis. Ovary (A); bursa copulatrix (B); spermatophore (C); testis (D).
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Figure 2. The population dynamics of C. medinalis trapped using food attractants and sex pheromones and the distribution of male age structure in different years and places. Dynamics of the number of C. medinalis trapped by food attractants and sex pheromones at Liling in 2020 (A); Zhangjiagang in 2020 (B); and Shaodong in 2021 (C); age distribution of males trapped at Liling in 2020 (D); Zhangjiagang in 2020 (E); and Shaodong in 2021 (F).
Figure 2. The population dynamics of C. medinalis trapped using food attractants and sex pheromones and the distribution of male age structure in different years and places. Dynamics of the number of C. medinalis trapped by food attractants and sex pheromones at Liling in 2020 (A); Zhangjiagang in 2020 (B); and Shaodong in 2021 (C); age distribution of males trapped at Liling in 2020 (D); Zhangjiagang in 2020 (E); and Shaodong in 2021 (F).
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Figure 3. Dynamics of the number of C. medinalis trapped using food attractants in different years and locations. Dynamics of the number of C. medinalis trapped using food attractants at Guigang in 2020 (A); Shaodong and Liling in 2020 (B); Zhangjiagang and Changzhou in 2020 (C); Xiangshan and Quzhou in 2020 (D); and Shaodong, Zhijiang and Taihe in 2021 (E).
Figure 3. Dynamics of the number of C. medinalis trapped using food attractants in different years and locations. Dynamics of the number of C. medinalis trapped using food attractants at Guigang in 2020 (A); Shaodong and Liling in 2020 (B); Zhangjiagang and Changzhou in 2020 (C); Xiangshan and Quzhou in 2020 (D); and Shaodong, Zhijiang and Taihe in 2021 (E).
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Figure 4. Analysis of the proportion of ovarian development levels of females of C. medinalis trapped at Guigang in 2020 (A); Liling in 2020 (B); Shaodong in 2020 (C); Changzhou in 2020 (D); Zhangjiagang in 2020 (E); Quzhou in 2020 (F); Xiangshan in 2020 (G); Shaodong in 2021 (H); Zhijiang in 2021 (I); and Taihe in 2021 (J).
Figure 4. Analysis of the proportion of ovarian development levels of females of C. medinalis trapped at Guigang in 2020 (A); Liling in 2020 (B); Shaodong in 2020 (C); Changzhou in 2020 (D); Zhangjiagang in 2020 (E); Quzhou in 2020 (F); Xiangshan in 2020 (G); Shaodong in 2021 (H); Zhijiang in 2021 (I); and Taihe in 2021 (J).
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Figure 5. Correlation between the index of ovarian development and male age of adult C. medinalis trapped using food attractants at Quzhou in 2020 (A); Xiangshan in 2020 (B); Shaodong in 2021 (C); and Zhijiang in 2021(D).
Figure 5. Correlation between the index of ovarian development and male age of adult C. medinalis trapped using food attractants at Quzhou in 2020 (A); Xiangshan in 2020 (B); Shaodong in 2021 (C); and Zhijiang in 2021(D).
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Figure 6. Correlation between the ovarian development level and mating time in attractant trapping of C. medinalis at Guigang in 2020 (A); Liling in 2020 (B); Zhangjiagang in 2020 (C); Quzhou in 2020 (D); Xiangshan in 2020 (E); Shaodong in 2021 (F); and Zhijiang in 2021 (G).
Figure 6. Correlation between the ovarian development level and mating time in attractant trapping of C. medinalis at Guigang in 2020 (A); Liling in 2020 (B); Zhangjiagang in 2020 (C); Quzhou in 2020 (D); Xiangshan in 2020 (E); Shaodong in 2021 (F); and Zhijiang in 2021 (G).
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Figure 7. Changes in the number of eggs within the ovarioles and the percentage of oviposition of the females of C. medinalis trapped using food attractants at Guigang (A) and Liling (B) in 2020.
Figure 7. Changes in the number of eggs within the ovarioles and the percentage of oviposition of the females of C. medinalis trapped using food attractants at Guigang (A) and Liling (B) in 2020.
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Table
Table 1. Monitoring locations and times for field trials in 2020–2021.
Table 1. Monitoring locations and times for field trials in 2020–2021.
Experimental YearExperimental Site/ProvinceExperimental Time (Month/Day)Longitude/Latitude
2020Guigang/Guangxi28 May–20 June109°43′48″/22°46′12″
2020Liling/Hunan8 July–8 Aug.113°31′12″/27°36′36″
2020Shaodong/Zhejiang3 July–21 July111°43′11″/27°18′36″
2020Zhangjiagang/Jiangsu16 July–12 Aug.120°31′48″/31°48′36″
2020Changzhou/Jiangsu17 July–18 Aug.119°29′24″/31°40′12″
2020Quzhou/Zhejiang23 July–25 Aug.119°11′24″/29°7′12″
2020Xiangshan/Zhejiang16 July–26 Aug.121°54′36″/29°24′36″
2021Shaodong/Zhejiang26 June–15 Aug.111°43′12″/27°18′36″
2021Zhijiang/Hunan19 June–14 Aug.109°40′48″/27°26′24″
2021Taihe/Jiangxi1 June–27 June114°52′48″/26°47′24″
Table
Table 2. Division criterion for the semi-major axis length of testes of 1–8-day-old male adults of C. medinalis.
Table 2. Division criterion for the semi-major axis length of testes of 1–8-day-old male adults of C. medinalis.
Adult Age (Day)Range of the Semi-Major Axis Length of Testes (μm)
1>421.1
2387.6–421.1
3367.3–387.6
4348.0–367.3
5327.9–348.0
6307.4–327.9
7277.8–307.4
8<277.8
Table
Table 3. The number of female and male C. medinalis trapped using food attractants at each experimental site in 2020 and 2021.
Table 3. The number of female and male C. medinalis trapped using food attractants at each experimental site in 2020 and 2021.
Experimental YearExperimental Site/ProvinceNumber of FemalesNumber of Malesχ2p
2020Guigang/Guangxi8001503214.59<0.001
2020Liling/Hunan17292413112.95<0.001
2020Shaodong/Hunan12722075192.65<0.001
2020Changzhou/Jiangsu5381591520.81<0.001
2020Zhangjiagang/Jiangsu1593976148.19<0.001
2020Quzhou/Zhejiang41967760.73<0.001
2020Xiangshan/Zhejiang493988165.45<0.001
2021Shaodong/Hunan24424173452.97<0.001
2021Taihe/Jiangxi1852071.240.270
2021Zhijiang/Hunan46464830.45<0.001
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Gao, L.; Yan, R.; He, W.; Wu, K. Use of Food Attractant to Monitor and Forecast Population Dynamics of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a Long-Distance Migratory Pest. Agronomy 2023, 13, 2141. https://doi.org/10.3390/agronomy13082141

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Gao L, Yan R, He W, Wu K. Use of Food Attractant to Monitor and Forecast Population Dynamics of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a Long-Distance Migratory Pest. Agronomy. 2023; 13(8):2141. https://doi.org/10.3390/agronomy13082141

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Gao, Lingyun, Ran Yan, Wei He, and Kongming Wu. 2023. "Use of Food Attractant to Monitor and Forecast Population Dynamics of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a Long-Distance Migratory Pest" Agronomy 13, no. 8: 2141. https://doi.org/10.3390/agronomy13082141

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